This invention relates to light-sensitive silver halide grains suitable for higher sensitization, preparation thereof and light-sensitive silver halide photographic materials.
The present invention further concerns silver halide emulsions having epitaxial hybridized silver salt crystals comprising developable silver salt crystals such as silver chloride, silver halochloride, etc. epitaxially junctioned onto silver iodobromide or silver bromide host crystals, which are excellent in sensitivity and developability.
In recent years, silver halide emulsions for photography are required to satisfy requirements, which are increasingly severe, namely to have high levels of performances such as high sensitivity, excellent graininess, high sharpness, low fog density and sufficiently high optical density.
As a high sensitivity emulsion responding to such requirements, silver iodobromide emulsions containing 0 to 10 mol % of iodine are well known in the art. And, as the methods for preparing these emulsions, there have been known the methods in which pH condition and pAg condition are controlled such as the ammoniacal method, the neutral method, the acidic method, etc. and the mixing methods such as the single jet method, the double jet method, etc.
On the basis of these known techniques, in order to accomplish further higher sensitization, improvement of graininess, high sharpness and low fog, very precise technical means have been investigated and practically applied. In the silver iodobromide emulsion aimed at by the present invention, studies have been done even about the emulsions controlled in concentration distributions of iodine within the individual silver halide grains, to say nothing of crystal habits and grain size distribution.
The most orthodox method for accomplishing photographic performances such as high sensitivity, excellent graininess, high sharpness, low fog density and sufficiently high covering power is to improve the quantum efficiency of a silver halide. For this purpose, the knowledges about solid physics have positively been applied. The study having calculated theoretically the quantum efficiency and speculating about the effect of grain size distribution is disclosed in, for example, the pretext of Tokyo Symposium concerning Progress in Photography in 1980, entitled "Interactions between Light and Materials for Photographic Applications", on page 91. According to this study, it is predicted to be effective for improvement of quantum efficiency to prepare a mono-dispersed emulsion by narrowing the grain size distribution. In addition, for accomplishing sensitization of a silver halide emulsion, in the step of chemical sensitization as described hereinafter in detail, it may be considered resonable to estimate that a mono-dispersed emulsion would be advantageous for accomplishing efficiently high sensitivity while maintaining low fogging.
For preparation of a mono-dispersed emulsion in industry, it is necessary to control the feeding rate of silver ions and halogen ions to the reaction system theoretically determined under sufficient stirring conditions, on the basis of pAg and pH strictly controlled, as disclosed in Japanese Provisional Patent Publication No. 48521/1979. The silver halide emulsions prepared under these conditions comprise the so-called normal crystal grains having (100) faces and (111) faces having either cubic, octahedral or tetradecahedral shapes at various proportions. And, higher sensitization has been known to be possible with such normal crystal grains.
On the other hand, a silver iodobromide emulsion comprising poly-dispersed twin crystal grains has been known in the art as a silver halide emulsion suitable for high sensitivity photographic film.
Also, in Japanese Provisional Patent Publication No. 113,927/1983 and others, a silver halide emulsion containing flat plate twin crystal grains is disclosed.
Although these techniques contribute to higher sensitization, demands for techniques capable of accomplishing further higher sensitization always exist.
On the other hand, as the technique for broadening exposure region, there has been known a technique to employ two or more kinds of emulsions with different sensitivities according to a means such as mixing of two or more kinds of emulsions with different average grain sizes.
By combination of the above higher sensitization technique and the technique for broadening exposure region, it is possible to obtain a light-sensitive photographic material having high sensitivity to some extent and a broad exposure region. However, development of techniques capable of realizing further higher demands in such aspects exists continuously.
On the other hand, a silver halide emulsion containing epitaxial hybridized silver halide crystals comprising polygonal crystals of silver iodide and silver chloride crystals formed through epitaxial junction onto the polygonal crystals is known to have both radiation sensitivity of silver iodide and rapid developability of silver chloride, and also release a relatively large quantity of iodide ions when developed, thereby giving a preferable photographic effect by the iodide ions, as disclosed in Japanese Provisional Patent Publication No. 10372/1978.
As the technique for improving the processability of this emulsion, European Patent Application No. 0,019,917 (published on December 10, 1980) discloses a silver halide emulsion containing crystals of a silver halide with less than 10 mole % of silver iodide formed through epitaxial junction onto silver halide crystals containing 15 to 40 mol % of silver iodide.
Further, the technique in which use of highly concentrated iodide is avoided in the host grains in the above emulsion is disclosed in Japanese Provisional Patent Publication No. 133,540/1984. In this technique, silver iodobromide with low content of silver iodide is employed as the host grains.
By use of these techniques, light-sensitive photographic materials capable of giving images excellent in sharpness through the edge effect can be obtained, but they are still low in sensitivity for practical application and therefore it is further required to develop a technique to enhance sensitivity.